Method for enabling a high torque/high speed brushless DC motor

Abstract

A high torque/high speed brushless DC motor system for controlling both the speed and torque of the motor including a rotor and a stator, the stator of the motor including a first, second and third winding. The system further includes means for sensing the position of the rotor and means for selectively configuring the first, second and third windings of the stator in a wye connection when the speed of the motor is less than a predetermined value and configuring the windings in a delta connection when the speed of the motor is greater than the predetermined value.

What is claimed is:  
     
       1. A method for controlling a brushless DC motor, said motor including a rotor and a stator, said stator comprising a first winding, a second winding and a third winding, said method comprising the steps of: 
       (a) configuring said first, second and third windings in a wye connection when a speed of said motor is less than a predetermined value; and  
       (b) configuring said first, second and third windings in a delta connection when the speed of said motor is greater than said predetermined value,  
       wherein step (a) further comprises:  
       sensing a position of said rotor using a first set of rotor position sensors, one rotor position sensor for each of said windings; and  
       synthesizing a rotating magnetic field in said windings by sequentially switching a current flow through said windings in response to said rotor position sensed by said first set of rotor position sensors; and  
       wherein step (b) further comprises:  
       sensing said position of said rotor using a second set of rotor position sensors, one rotor position sensor for each of said windings; and  
       synthesizing a rotating magnetic field in said windings by sequentially switching said current flow through said windings in response to said rotor position sensed by said second set of rotor position sensors.  
     
     
       2. The method of  claim 1 , wherein step (a) comprises: 
       controlling a first switch means to connect a first terminal of said first winding to a first drive signal source and a second terminal of said first winding to a common node;  
       controlling a second switch means to connect a first terminal of said second winding to a second drive signal source and a second terminal of said second winding to said common node; and  
       controlling a third switch means to connect a first terminal of said third winding to a third drive signal source and a second terminal of said third winding to said common node.  
     
     
       3. The method of  claim 1 , wherein step (b) comprises: 
       controlling a first switch means to connect a first terminal of said first winding to a first drive signal source and a second terminal of said first winding to a second drive signal source;  
       controlling a second switch means to connect a first terminal of said second winding to said second drive signal source and a second terminal of said second winding to a third drive signal source; and  
       controlling a third switch means to connect a first terminal of said third winding to said third drive signal source and a second terminal of said third winding to said first drive signal source.  
     
     
       4. The method of  claim 1 , wherein said first winding has a first terminal connected to a first drive signal source, said second winding has a first terminal connected to a second drive signal source, said third winding has a first terminal connected to a third drive signal source, and wherein step (a) comprises: 
       controlling a first switch means for connecting a second terminal of said first winding to a common node;  
       controlling a second switch means for connecting a second terminal of said second winding to said common node; and  
       controlling a third switch means for connecting a second terminal of said third winding to said common node; and  
       wherein step (b) comprises:  
       controlling said first switch means for connecting said second terminal of said first winding to said second drive signal source;  
       controlling said second switch means for connecting said second terminal of said second winding to said third drive signal; and  
       controlling said third switch means for connecting said second terminal of said third winding to said first drive signal source.  
     
     
       5. The method of  claim 1  wherein said rotor position sensors comprise Hall type magnetic sensors. 
     
     
       6. The method of  claim 1  wherein a torque of said motor is higher at speeds lower than said predetermined value than at speeds greater than said predetermined value. 
     
     
       7. A method for controlling a brushless DC motor, said motor including a rotor and a stator, said stator comprising a first winding, a second winding and a third winding, said method comprising the steps of: 
       (a) configuring said first, second and third windings in a wye connection when a speed of said motor is less than a predetermined value; and  
       (b) configuring said first, second and third windings in a delta connection when the speed of said motor is greater than said predetermined value,  
       wherein step (a) further comprises:  
       sensing a position of said rotor using a set of rotor position sensors, one rotor position sensor for each of said windings; and  
       synthesizing a rotating magnetic field in said windings by sequentially switching a current flow through said windings in response to said rotor position sensed by said first set of rotor position sensors; and  
       wherein step (b) further comprises:  
       sensing said position of said rotor using said rotor position sensors; and  
       synthesizing a rotating magnetic field in said windings by sequentially switching said current flow through said windings in response to said rotor position sensed by said rotor position sensors, wherein a phase of said rotor position sensors in step (a) and step (b) differs by a phase shift.  
     
     
       8. The method of  claim 7  wherein the phase of said rotor position sensors in step (a) and step (b) differs by the phase shift of about thirty degrees electrical. 
     
     
       9. The method of  claim 7  wherein said rotor position sensors comprise Hall type magnetic sensors. 
     
     
       10. The method of  claim 7  wherein a processor controls the phase shifting of said rotor position sensors.